Water masses in the Gulf of Aden

Hydrographic data collected from Gulf of Aden since 1920 have been compiled to identify and refine the definitions of water masses in the Gulf of Aden (GA) and to describe their spatio-temporal variability. Four water masses have been identified based on their θ-S characteristics. The Red Sea Water (RSW) that flows from the Red Sea is the most prominent water in the GA; this occupies about 37% of the total volume of Gulf of Aden. The Gulf of Aden Surface Water (∼3%) forms as a mixture of local water and the water from western Arabian Sea during winter and Red Sea surface water during summer. The intermediate water, identified as Gulf of Aden Intermediate Water (GAIW), occupies about 9% of the total volume of GA; a characteristic salinity minimum is associated with it at σ_θ=26.50 kg m⁻³. The northward spread of sub-tropical subsurface water from the south appears to be the major source of GAIW. The bottom water, named Gulf of Aden Bottom Water, showed the least variability. It was formed due to the mixing of Red Sea Water and water of southern origin. Mixing triangles have been used to analyze the composition of water in the GA.     

Unplanned urban growth: land use/land cover change in the Guwahati Metropolitan Area,India

Unplanned urban growth, particularly in developing countries has led to changes in land use/land cover (LULC). Numerous Indian cities face problems of unplanned LULC change due to nominal or non-existent planning efforts compounded by rapid urban population growth. The Guwahati Metropolitan Area (GMA) is one such urban centre. The present study assesses the trajectories of LULC change using Landsat imageries acquired in 1976, 1989, 2002 and 2015. Natural and semi natural vegetated area and artificial and natural water bodies decreased while built-up areas, cultivated and managed areas, and natural and semi natural non-vegetated areas increased. The built-up area increased from 23.9 in 1976 to 115.1 km² in 2015 becoming the dominant land cover class accounting for 41.8% of the total geographical area. During this period, natural and semi natural vegetated land were reduced by 88.9 km² at an annual rate of 2.2 km². Over the years there was an increasing trend of built-up land and cultivated and managed areas in the peripheral areas of the city while natural and semi natural vegetated land diminished. Consequently, as in many other developing countries, there is an urgent need for the governmental authorities and other stakeholders to implement effective urban planning policies.     

Collision strength dependence of solar emission lines from carbon- and nitrogen-like ions

We have calculated the normalized populations of ground and first excited state levels in carbon-and nitrogen-like ions in an optically thin medium, under steady conditions, by using: (i) the incident electron energy dependent collision strengths and (ii) the constant collision strength (CCS) values at the incident electron energyE. The assumption of CCS affects the line-intensity ratio within the observational uncertainties. It is concluded that to calculate the intensity ratios for solar lines one can alternatively use CCS at electron energyE.     

Genetic architecture of three Turbinella pyrum varieties (Linnaeus, 1758) from the southeast coast of India

The genetic diversity and variation of three pseudo‐species of the commercially important Indian conch Turbinella pyrum from the southeast coast of India were studied. A total of 88 individuals was genotyped at 12 loci and differences in the genetic diversity among genetic groups were correlated with known population histories. The study identified 535 alleles and all the studied loci were highly polymorphic. The number of alleles ranged between four and 29 with a global mean of 14.861. The global means of the observed and expected heterozygosities were 0.774 and 0.891, respectively. The estimated within‐population inbreeding value (F_IS = 0.131) indicated a shortfall of heterozygosity in the populations. An analysis of molecular variance showed that 5% of the total variation was due to differences between genetic groups. The Bayesian approach revealed strong distinctiveness in the three genetic groups studied. Overall microsatellite analysis revealed less genetic diversity in all studied genetic groups and significant genetic variation among the three pseudo‐species. The study highlights the significant distinctiveness of the pseudo‐species of T. pyrum and the need for appropriate conservation efforts in order to prevent further losses of their genetic diversity.     

Identification of groundwater drought prone zones in Pedda vagu and Ookachetti vagu watersheds,tributaries of the Krishna River,India

The Pedda vagu and Ookachetti vagu watersheds located in the semi-arid regions of Mahabubnagar district are highly dependent on groundwater for irrigation owing to unreliable rainfall and over extraction of groundwater. The present study has been conducted to identify spatio-temporal groundwater droughts and drought-prone zones. Temporal groundwater droughts have been determined using a standardized water-level index along with spatial groundwater droughts using spline interpolation in Geographic Information Systems. The study shows that the groundwater droughts varied among the stations during the observation period, i.e. 1998–2011. However, the spatial assessment shows that the region as such experienced more mild groundwater droughts except during severe meteorological drought years (1998, 2002, 2004 and 2008); this indicates that the region has good scope for groundwater exploitation during dry spells and initial stages of droughts. Therefore, it is critical to have plans for the development of groundwater to cope with drought.     

A generalized model for geosynthetic reinforced railway tracks resting on soft clays

The present study pertains to the development of a foundation model for predicting the behavior of geosynthetic reinforcement railway track system rested on soft clay subgrade. The ballast and sub‐ballast layers have been idealized by Pasternak shear layer. The geosynthetic layer is represented by a stretched rough elastic membrane. Burger model has been used to characterize the soft clay subgrade. Numerical solutions have been obtained by adopting the finite difference scheme combined with non‐dimensioning the governing equations of the proposed model. The results confirm that the present model is quite capable of predicting the time‐dependent settlement response of geosynthetic reinforcement railway track system placed on soft clay subgrade. The surface settlement profile and mobilized tensile load of geosynthetics has been evaluated by considering variation in the wheel load, sleeper width, thickness of ballast and sub‐ballast layers and shear modulus of ballast and sub‐ballast layers. It has been observed that an increase in the sleeper width by 24% results in the reduction in central settlement and mobilized tensile load by 6.5% and 20.1%, respectively. It was found that with a 50% increase in the thickness of the ballast layer, the central settlement has decreased by 7.3% and the mobilized tension at the zone of maximum curvature has increased by 24.6%. However, with an increase in the thickness of the sub‐ballast layer, a considerable reduction in both central settlement and the mobilization of tension on geosynthetic has been noticed. The pattern of variation of settlement and mobilized tension for an increase in the shear modulus of ballast and sub‐ballast material was found to be almost similar. Copyright © 2014 John Wiley & Sons, Ltd.     

Plant remains from the Laisong Formation of Manipur

Some plant remains are described from the Laisong Formation (Barail Group) of Thoubal and Senapati districts of Manipur. The flora is diverse comprising gymnospermous, monocotyledonous and dicotyledonous forms and indicates tropical to subtropical climate in the vicinity of the area during the deposition of the host rocks.     

Upper gondwana succession of the Rewa Basin,India: Understanding the interrelationship of lithologic and stratigraphic variables

The current work attempts to address a century old problem regarding the stratigraphic disposition of the Upper Gondwana succession of the Rewa basin based on geological mapping and litholog preparation along well exposed transects. The proposed Upper Gondwana stratigraphy of the Rewa basin comprises a continuous and thick package of Triassic sediments unconformably overlain by the Jurassic Parsora Formation. The Triassic succession consists of a basal Pali Formation, an intermediate and newly designated Karki Formation and the overlying mud-dominant Tiki Formation. These formations are well defined based on physical attributes such as lithology, textures and sedimentary structures, and are easily distinguishable in the field. Based on stratigraphic correlation and fossil content, a Lower-Middle Triassic age has been assigned for the Pali and Karki formations, while the Tiki Formation is Upper Triassic (Carnian) in age. Preliminary observations based on lithological characteristics, sand body geometry and sand: mud ratios suggest that within a fluvial setting there were considerable changes in environments of deposition through time, especially during Triassic to Jurassic transition.